1. Field of the Invention
The present invention relates to an electroacoustic transducer which is adapted to be mounted on a printed circuit board.
2. Description of the Related Art
Many of electroacoustic transducers such as speakers and microphones are adapted to be mounted on a printed circuit board of electronic equipment such as a mobile phone. In such an electroacoustic transducer, a terminal plate is fixed on a casing at a position away from a casing surface opposite the printed circuit board (opposite surface). Then a conductive member is required to allow the terminal plate to be electrically connected to a conductive portion of the printed circuit board.
A coil spring is conventionally known as one of such conductive members. The coil spring is placed between the terminal plate and the conductive portion of the printed circuit board in a resiliently compressed state. See Japanese publication A-2001-242871.
FIG. 8(a) shows part of the conventional electroacoustic transducer having such coil spring. A cylindrical recess 102b is formed on a casing 102, extending from an opposite surface 102b to a terminal plate 104. A through hole 104a is formed on the terminal plate 104 at a position corresponding to the cylindrical recess 102b. A coil spring 106 has a protruding pin 106a extending in the axial direction from an end of the coil spring 106. The protruding pin 106a is passed through the through hole 104a to be fixed to the terminal plate 104 by solder 108.
Such conventional electroacoustic transducer, however, possibly causes a problem as described below depending on how it is mounted on the printed circuit board.
In an assembly of a mobile phone, the top surface of the casing 102 (the counter surface of the opposite surface 102a) of the electroacoustic transducer is adhered to the inner surface of the upper case of the mobile phone by a double-stick tape, and then the electroacoustic transducer and the upper case of the mobile phone are pressed against the printed circuit board to be mounted thereto. It is very likely that the coil spring 106 is horizontally displaced with respect to the printed circuit board, generating stress concentration at the base part of the protruding pin 106a of the coil spring 106.
FIG. 8(b) shows a state where the casing 102 is displaced leftward with respect to the printed circuit board 2 with the coil spring 106 resiliently compressed against the printed circuit board 2. The protruding pin 106a soldered to the terminal plate 104 is also displaced leftward as the casing 102 is displaced so. The other end of the coil spring 106, however, remains in the place since it is compressed against the printed circuit board 2. Then the coil spring 106 is suffered from horizontal distortion as shown in the figure, exerting a larger bending moment to the base part of the protruding pin 106a (a surrounded area by dotted line) and generating stress concentration thereon.
The coil spring is likely to be broken during the assembling process, or durability of the coil spring is deteriorated.
An object of the present invention is to provide an improved structure for accommodating and supporting a coil spring inside the cylindrical recess while fixing it to neither the terminal plate nor the casing.
The present invention relates to an electroacoustic transducer adapted to be mounted on a printed circuit board comprising:
a casing;
a terminal plate fixed on the casing at a position away from a casing surface opposite the printed circuit board; and
a coil spring for making electrical connections between the terminal plate and a conductive portion of the printed circuit board when the electroacoustic transducer is mounted on the printed circuit board;
wherein, a cylindrical recess is formed on the casing so as to extend from the casing surface to the terminal plate;
the coil spring has a coil length longer than that of the cylindrical recess by a predetermined dimension, and a coil diameter smaller than the inner diameter of the cylindrical recess by a predetermined dimension; and
the coil spring is accommodated and supported in the cylindrical recess while it is fixed to neither the terminal plate nor the casing.
Any type of the xe2x80x9celectroacoustic transducerxe2x80x9d is applicable such as speaker, buzzer, microphone, and receiver as far as it is adapted to be mounted on the printed circuit board.
Any type of the xe2x80x9cprinted circuit boardxe2x80x9d is applicable as far as a conductive portion is formed thereon to make electrical connections with the terminal plate via the coil spring.
Any type of the xe2x80x9ccasingxe2x80x9d is applicable as far as the terminal plate is fixed thereon at a position away from the casing surface opposite the printed circuit board. The xe2x80x9ccasing surface opposite the printed circuit boardxe2x80x9d is a surface facing the printed circuit board when the electroacoustic transducer is mounted on the printed circuit board. After the electroacoustic transducer is mounted on the printed board, the surface may be contact with the printed circuit board or may be away from it by certain distance.
Any type of the xe2x80x9ccylindrical recessxe2x80x9d is applicable as far as it extends from the casing surface opposite the printed circuit board to the terminal plate. It does not always require a circumferential wall formed entirely.
Any type of the xe2x80x9ccoil springxe2x80x9d is applicable as far as it is made of conductive material and it is accommodated and supported in the cylindrical recess while it is fixed to neither the terminal plate nor the casing. The phrase xe2x80x9caccommodated and supported in the cylindrical recessxe2x80x9d means that the coil spring does not come off the cylindrical recess in a no-load state and part of the coil spring is accommodated in the cylindrical recess. The coil spring is supported but fixed to neither the terminal plate nor the casing.
The xe2x80x9ccoil lengthxe2x80x9d is not limited to a specific value. It may be any value as far as it is longer than the length of the cylindrical recess and long enough for surely making electrical connections between the terminal plate and the conductive portion of the printed circuit board when resiliently compressed. The xe2x80x9ccoil diameterxe2x80x9d is not limited to a specific value. It may be any value as far as it is smaller than the inner diameter of the cylindrical recess and it allows the coil spring to be compressed and shifted in the cylindrical recess.
According to the present invention, since the coil spring is accommodated and supported in the cylindrical recess while it is fixed to neither the terminal plate nor the casing, the coil spring is free from any stress concentration even if external force is exerted.
In state that the coil spring is pressed against the printed circuit board, any horizontal displacement between them would not cause stress concentration on the coil spring since the coil spring is only horizontally shifted in the cylindrical recess until the coil portion hits against the wall of the cylindrical recess. This prevents a breakage of the coil spring during the assembling process and also a possible deterioration thereof after the assembling process.
As described above, breakage or damage of the coil spring is prevented even when it is used as a conductive member for making electrical connections between the terminal plate and the conductive portion of the printed circuit board,
The present invention eliminates the need for soldering of the coil spring to the terminal plate, simplifying the manufacturing process of the electroacoustic transducer.
The present invention eliminates the need for positioning of the coil spring with respect to the cylindrical recess to insert the protruding pin into the through hole for soldering, simplifying the manufacturing process of the electroacoustic transducer.
The present invention eliminates the risk of soldering heat which is likely to deform the resin members or portions near the terminal plate.
Eliminating the need for soldering provides an environmental PB-free product.
According to the present invention, a through hole is formed on the terminal plate at an exposed portion above the cylindrical recess. The inner diameter of the through hole is larger than a wire diameter of the coil spring by a predetermined dimension. A protruding pin is axially extended from the coil spring at the side of the terminal plate to be passed though the through hole of the terminal plate, and the leading portion of the protruding pin is bent.
By bending the leading portion, the protruding pin is hooked on the terminal plate, thus preventing the coil spring from coming off the cylindrical recess. The coil spring is accommodated and supported in the cylindrical recess with an extremely simple structure.
The xe2x80x9cpredetermined dimensionxe2x80x9d is not limited to a specific value. In order to definitely guard against a horizontal distortion of the coil spring, however, the dimension is desirably set to such value as to prevent the protruding pin from hitting against the wall of the through hole until the coil portion hits against the wall of the cylindrical recess.
According to the present invention, a through hole is formed on the terminal plate at an exposed portion above the cylindrical recess. The inner diameter of the through hole is larger than a wire diameter of the coil spring by a predetermined dimension. A protruding pin is axially extended from the coil spring at the side of the terminal plate to be passed though the through hole of the terminal plate. A ring member is disposed between the terminal plate and a leading portion of the protruding pin, having a center hole of smaller diameter than the through hole for allowing the protruding pin to pass through. The leading portion of the protruding pin is hooked or fixed on the ring member.
The leading portion of the protruding pin may be bent to be hooked on the ring member. Alternatively, the leading portion may be adhered to the ring member. Interposing the ring member eliminates the need for bending the leading portion at a great deal of angle, thus effectively preventing the protruding pin from coming off the terminal plate.
According to the present invention, the coil diameter of the coil spring may be smaller at the side of the printed circuit board than at the side of the terminal plate. A ring portion may be provided in the cylindrical recess at the side of the printed circuit board to make the inner diameter of the cylindrical recess smaller than the coil diameter at the side of the terminal plate.
This structure eliminates the need for a through hole in the terminal plate. The embodiments include the following structures. The coil spring may be gradually reduced in diameter from the side of the terminal plate to the side of the printed circuit board. The coil spring may be tapered in diameter from the side of the terminal plate to the side of the printed circuit board. The coil spring may comprise a cylindrical portion at the side of the terminal plate and a tapered portion at the side of the printed circuit board.
The ring portion may be separately provided or may be integrally formed with the casing by plastic deformation of the casing. When a separate ring member is used, it is press fit into the cylindrical recess.